Welding apparatus



May 26, 1953 J. R. PARSONS WELDING APPARATUS 2 Sheets-Sheet 1 FiledApril 2, 1948 John E param BY W l ATTORNEY y 25, 1953 .1. R. PARSONSWELDING APPARATUS 2 Sheets-Sheet 2 Filed April 2, 1948 INVENTOR John RParsons.

ATTORN EY Patented May 26, 1953 UNITED STATES PATENT OFFICE 1 WELDINGAPPARATUS John R. Parsons, Kenmore, N. Y., assignor to WestinghouseElectric Corporation, East Pittsburgh, Pa", a corporat'ionofPennsylvania Application April 2, 1948, Serial No. 18,699

9 Claims. 1

This invention relates to electric discharge apparatus and hasparticular relation to electronic timing systems for controlling thesupply of power from a source to a load.

Resistance welders have, in the prior art, generally operated fromcommercial alternating current power lines, and have derived power froma single phase of such lines, despite the fact that most power lines forindustrial electricity are of the three phase variety. Such operationhas generally been considered satisfactory, for relatively lower powerwelding.

As the thickness of material to be welded increases, the power drawnfrom the line increases exponentially. Additionally, and especially inwelding steel, a reactive component is introduced into the welding loadby the reactance of the secondary winding of the Welding transformer,which links with the steel being welded. The reactance of the secondarybecomes higher, generally, than the resistance of thesecondary,.including the weld, so that power factors of as low as 25%are common. Still ,a further factor to be considered in welding heavymaterial, requiring extremely high welding current, is skin effect inthe secondary circuit, due to the flow of alternating current in thesecondary circuit. One does not ordinarily consider skin effect to besignificant at sixty cycles per second but under the conditions ofextremely high current and extremely low direct current resistanceencountered in welding transformer secondaries, secondary resistance isdetermined in considerable part by skin effect, and the resistance ofthe secondary circuit cannot, accordingly, be lowered indefinitely byordinary engineering expedients. Since thecurrent required for weldingis fixed, thekilowatt demand of the welding machine is proportional tothe resistance of the secondary circuitof the welding transformer,resulting in high kilowatt demand.

Single phase welding has, accordingly, the-following limitations:

1. it causes unbalance of the three phase system from which power isdrawn;

2. it creates a high kilo volt ampere demand at low power factor;

3. it creates a high kilowatt demand. 1

It is extreme'lydesirable to decrease the kiloload, thereby decreasingthe cost of operation of the welder as well as the total cost of aninstallation designed :to perform given welding functions. It is-furtherextremely desirable that the 'welder operate at high power factor andconstitute a balanced three phase load forsimiiar economic reasons.

When direct current is applied to the primary winding of a single phasetransformer, there is created in the iron core of the transformer amagnetic field of increasing value, until the iron saturates. Thevariation of magnetic field induces a voltage in the secondary of thetransformer, and consequently a current, if the secondary circuit isclosed. When the secondary current reaches its maximum value the ratio.of primary to secondary current is determined by the turns ratio of thetransformer, and when the primary is interrupted the secondary currentdecays. A succeeding current impulse may be in the'opposite direction,so that two time-adjacent impulses constitute a low frequency cycle ofcurrent. This reduces skin effect, since the effective welding frequencyis reduced, which in turn lowers the conductivity of the Weldingtransformer secondary, and thereby the kilowatt demand. Further,secondary reactance is decreased, which raises the power factor of thesystem.

It is further found, as an ancillary advantage, that the slow rise ofwelding current causes the current to distribute itseli in the weld moreevenly, resulting in better welds and no intense local heating orsplitting,

The system of direct current welding, above briefly described, lendsitself .to operation from a three phase line, deriving current from allthe phases of the line, since voltage waves in the various linesoverlap, and accordingly half-wave rectification of three phase currentsand superposition thereof in a single welding secondary providesimpulses of direct current of an overlapping and hence substantiallycontinuous character, each phase of the line providing current fordegrees of each cycle.

The provision for reversal of the direct current welding current, andcontrol of the amplitude of that current, may comprise arcdischarge'devices, and specifically ignitrons, connected in inverseparallel, in the separate phases of the three phase line, eachcontrolled by a firing tube to which is applied firing signal inpredetermined phase, which may be adjustable.

Timingarrangements may be provided for controlling the operation of thesystem, enabling sequencing of the complete welding operation, andcontrolling the on-ofi times of the are dis-- charge devices duringwelding to provide low frequency operation in selected and adjustableperiods of current flow, that is, in alternately opposite directions forpredetermined time intervals .in each direction.

I It follows that the development of three phase to single phase weldingequipments, wherein the 3 single phase welding current is of lowfrequency, will lead to increased utility of welding equipment, enablimsuperior welding, and particularly more economical operation andconstruction of welding equipment operating at high power.

It is, accordingly, an object of the present invention to provide anovel system of electric welding.

It is a further object of the invention to provide a novel system of D.C. welding.

It is still a further object of the invention to provide a novel systemof welding which utilizes the three phases of a three phase power lineas a source of welding current.

It is another object of the present invention to provide a system ofdirect current welding which establishes a load on all the phases of athree phase line.

It is a more specific object of the invention to provide a. system ofdirect current welding where- It is another broad object of the presentinvention to provide a novel. system for controllably transferring powerfrom a three phase power supply to a single phase load, by causingsuccessive increments of current how in opposite directions in the load,each increment of current enduring for a controllable time interval, andderiving from a plurality of phases of the three phase power supply.

It is still another object of the present invention to provide a systemfor supplying power to a load from an alternating current sourc indiscrete unidirectional pulses of preselectable duration and alternatelyopposite directions of fiow.

It is a further object of the invention to provide a system of supplyingalternating current to a load from an alternating current source, inpulses having a lower frequency than the frequency of the source, thefrequency of the current supplied to the load being adjustable.

It is, still further, an object of the present invention to provide anovel system of controlling arc discharge devices connected in a threephase line.

Another object of the invention resides in the provision of a threephase system utilizing inverse parallel connected arc discharge devicesto control the flow of current to a load circuit, and having noveltiming circuits for establishing the durations of ciurent fiowalternately in different predetermined groups of the arc dischargedevices.

It is an ancillary object of the invention to provide an electricalinterlock system for interconnected arc discharge devices, forpreventing discharge or" one of the discharge devices in response todischarge of another, whereby to prevent simultaneous firing ofassociated discharge devices.

It is a further ancillary object of the invention to provide a novelelectronic timing circuit for two groups of arc discharge devices, forestablishing alternate operation of the groups each for a preselectedtime and for further establishing the total time of operation of bothgroups together.

'wound on mutually isolated cores.

It is still a further ancillary object of the present invention toprovide a single electronic timing circuit for establishing the durationof a total tim of operation of controlled devices, and for sub-dividingthe total time into discrete subintervals of time.

Briefly described, in accordance with the present invention, power isapplied to a single phase welding load, over a three phase to singlephase transformer, from a three phase line, a pair of back to backdischarge valves, specifically ignitrons, being connected between eachphase of the line and a primary or the transformer for controlling andtiming the transfer of power.

The ignitrons are fired by grid-controlled firing valves, specificallythyratrons, in conventional fashion, the firing valves being suppliedcontinuously with appropriate control voltage from the three phase line,over a phase shifter, which serves to determine the times of firing ofthe firing valves, and consequently of the discharge valves, withrespect to the phases of the voltages supplied to the discharge valvesby the line.

The discharge valves and their associated firing valves may be grouped,each group containing one discharge valve of each of the back to backpairs, and the valves of each group operating to transfer current in thesame direction into the welding load. Accordingly, the discharge valvesof one group fire in succession, at 120 phase intervals, until theoperation of the group is discontinued by a control signal, thedischarge valves of the remaining group firing in succession aftercompletion of the firing of the valves comprising the first group, untilthe operation of the remaining group is in its turn discontinued.

The firing valves of each group are supplied with blocking potential,which may be applied to the firing valves of each group selectively, orto the firing valves of both groups simultaneously.

Additionally, each discharge valve is provided with an auxiliary anode,which together with the cathode of the valve provides eifectively aswitch, which is open when the discharge valve is not fired, and whichis closed effectively by the arc discharge in the valve when the latteris firing. The auxiliary anode circuits of the various discharge valvesare utilized to control a special interlock circuit, constituting oneimportant feature of the present invention, and which is arranged asfollows.

A special transformer is associated with each group of discharge valves,each transformer being provided with two separate cores which have nomagnetic flux interlinkage. The auxiliary anode to cathode circuit ofeach discharge valve of a group is connected each across a separateauxiliary winding which links with both cores simultaneously, and twofurther windings are provided, one of which, called the primary winding,links one of the cores only, and the other of which, called thesecondary winding, links the other of the cores only. Normally then,while the associated discharge valves are not firing, transfer of energybetween the primary and the secondary windings does not take place,these windings having no mutual inductance since they are When, however,any one of the associated discharge valves is firing a circuit is closedfor the associated auxiliary windings, which links both cores, andtransfer of energy from the primary to the secondary winding takes placevia the auxiliary winding.

The primary windings of the special transformers associated respectivelywith the dischargevalve groups are'energized at all times. The secondarywinding of the transformer associated with the firstgroupof valves'isconnected to energize a circuit which develops hold-off bias for all thefiring valves of the second group of discharge'valves, and thesecondarywinding of the transformer associated with the secondgroup ofvalves is connected to energizea circuit which develops hold-off biasfor all the firing valves of the first group of discharge valves.

Accordingly, whenever any discharge valve of thefirst group is firing,no valve of the second group is enabled to fire, and alternately, whenany discharge valve of the second group is firing no valve of the firstgroup is'a'ble to fire. The system of the present invention accordinglyprovides positively for the alternate firing of the separate groups ofvalves, and for completion of a then occurring cycle of firing-of adischarge deviceof one'group before any valve of the alternate group maycommence firing.

Sequencing circuit areprovided for controlling squeeze-time, weld-time,hold-time and off-- time, and a further special circuit is provided,

which, in conjunction with the circuit for estab- 1ishing weldtime-intervals, establishes sub-intervals of the weld-time, and controlsthe are dis charge devices to provide welding current in oppositedirections during alternate sub-intervals.

Total weld time is established in terms'of the charge on a weld timecondenser connected in the grid circuit of a gaseous control tube toprovide hold-off bias therefor, and an auxiliary discharge circuit isprovided including an auxiliary condenser of smaller capacitythan theweld time condenser, which abstracts from the weld time condensersuccessive increments of charge, until the latter is completelydischarged and the associated gaseous control tube fires, terminatingthe weld time. Successive increments of charge are removed from the weldtime condenser by means of a frequency control arrangement, comprising agaseous control tube having a hold-off timing circuit, the lattercomprising a timing condenser and separate charge and discharge timingcircuits therefor, which are separately adjustable. The time constantsof the charge and discharge circuits are adjusted normally to provideequal on and off times for the frequency control tube, by manuallyadjusting each of a pair of control potentiometers, one in the chargeand the other in the discharge circuit of the timing'condenser. A relayis provided in the plate circuit of the control tube, which, whenenergized, completes the charging circuit for the timing condenser, andwhich when deenergiz'ed completes the discharge circuit therefor.

Accordingly, the frequency control tube is turned off and on inaccordance With'its own law of operation, at controllable intervals.

Each energization' of the frequency control relay additionally completesthe circuit which abstracts an increment of charge from the weld time"control condenser, so that, after a predetermined number of cycles oflow frequency operation of the frequencycontrol relay, the weld timecondenser completes its discharge, firing the weld time control tube,and initiating 'a' hold operation in the operating sequence.

Contacts are provided, which are closed and opened in alternation bythefrequency control relay, and which serve alternately to apply energy tothe off-bias control or hold circuits of the firing valves associatedwith the separate groups of arc discharge welding power controltubes,o'r ignitrons, of the system, applying hold off signal to one biascontrol circuit, while the frequency control relay is energized, and tothe other while the frequency control relay is deenergized, In thismanner low frequency alternatingcurrent, or successive pulses ofalternately reversing direct current, are applied to the welding load,substantial in synchronism-with the operations of the frequency controlrelay.

After a predetermined number of complete cycles of low frequency weldingcurrent have passed through the welding load, and the weld time'control'tube fires, contacts are closed which complete simultaneously circuitsfor both off-biasingor hold circuits which control the ignitron firingtubes, preventing further operation of both groups of ignitrons andterminating the welding interval or weld time. The novel features whichI consider to becharacteristic of my invention are set forth withparticularity in the appended claims. The invention itself, however,both as to its organization and its method of operation, together withadditional objects and advantages thereof, will best be understood fromthe following descriptionof a specific embodimei'it thereof, especiallywhen read in connection with the accompanying drawings, wherein:

Figures 1A. and 1E, taken together, provide a diagrammatic circuitdiagram of an embodiment of the invention, and

2 a diagrammatic representation ofa special circuit control transformerutilized in the invention of Figures 1A and 1B.

Referring now to Figure 1A of the drawings, the reference numerals Li L2and L3 identify the lines of a three phase power source, the separatephases of which supply power to ignitrons l'I'U and EU, ZTU and BTU, BTUand GTU, arranged in back to back pairs, one pairacross each phase ofthe source, to separate primary windings H, i2, E3 of a transformer Tthe single secondary winding Hi or which supplies power to a weldingload L.

Each of the ignitrons iTU BTU, inclusive, is controlled by a thyratron,the respective thyratrons being identified by the designations lC'I'ECT, and being connected each in series between the anodes and theigniting rod of an associated ignitron, so that firing of any thyratroninitiates firing of the associated'igni-tron.

Firing voltage is supplied to the control grids of the thyratrons iCTESCT over transformers IT 6T, respectively, the various transformersbeing connected via a variable phase shifter PS to the lines Li, L2 andL3. The variable phase shifter PS serves to vary the phase of the Voltages applied to the control grids of the respective thyratrons lCT ECT',with respect to the voltages applied to the anodes thereof directly fromthe lines Ll, L2, L3, whereby to vary the firing times of the thyratronsICT GCT, and of the ignitrons iiU BTU, and thereby the average powersupplied to the welding load L.

It will be realized that the utilization of ignitrons and thyratrons inthe present invention involves a matter of choice of circuit elements,and that other types of electronic discharge devices may be employed inpracticing the invention, without departing from the true spiritthereof; Accordingly, the valves iCT BCT will be referred to hereinafteras firing valves, for "the sake"v of generality, since these valvesserve to initiate firing of the ignitrons. The ignitrons themselvesmaybe referred to as arc discharge devices or valves, it being theirfunction to pass current to the welding load. In particular, it will beevident that thyratrons may be substituted for the ignitrons ITU STU,for operating into relatively light welding loads, and that hard orpurely electronic valves may be utilized in place of the thyratrons ICTGOT, if the required firing current is of sufiiciently low value.

An additional control is provided in the control grid circuit of each ofthe thyratrons ICT GOT, comprising in each case a bias circuit includinga parallel combination of resistance RI and condenser Cl, across whichis connected a rectifier unit RX, the separate rectox units RX beingsupplied with power by transformers 1T |2T inclusive, associatedrespectively with the thyratrons iCT SOT. Upon energization of any oneof the transformers 7T |2T, the rectox unit connected across thesecondary of the transformer develops a cut-ofi: bias voltage for theassociated thyratron i-CT BCT, preventing firing thereof in response tofiring voltage developed by the firing transformers |T 6T, respectively.

In the system of the present invention the set of ignitrons |TU, 2TU andSTU are to be fired in sequence for a period, after which the set ofignitrons 4TU, 5TU and STU are to be fired in sequence for an equalperiod. In accordance with the invention an interlccl: is provided whichoperates in response to firing oi any one of either group of ignitronsto prevent firing of the ignitrons of the alternate group. For thispurpose I provide within the envelope of each of the ignitrons ITU STUan auxiliary anode Hi from which current may be derived, when and onlywhen, the ignitron of which it forms part is firing. Separate controlwindings l6, l7 and I8 or" a transformer |3T are connected across theauxiliary anode to cathode circuits of the ignitrons |TU, 2TU and STUrespectively; and separate control windings |9, 26, iii of a furthertransformer |4T are connected across the auxiliary anode to cathodecircuits of the ignitrons 4Tb, STU and BTU, respectively. A. C. power issupplied to transformers |3T and MT over primary windings 22 and 23respectively, which are connected in parallel across terminals 24, 25,which are coupled permanently to one phase of the three phase supply, aswill be disclosed in greater detail hereinafter. A secondary 26associated with transformer |4T supplies power to transformers 1T, 8T,and ST in parallel, over leads 2! and 28. Transfer of power betweenprimary 23 and secondary 26 of transformer |4T occurs, however, only inthe presence of current in one of control windings i9, 20, 2! forreasons provided hereinafter.

Alternatively, when any one of ignitrons |TU, ZTU, and 3TU conduct, theauxiliary anodes l5 thereof apply power to an associated control windingI6, I! or |8 of transformer |3T enabling the transfer of energy betweenprimary 22 and secondary 29 of transformer |3T, and the consequenttransfer of energy to transformers HIT. HT and |2T, associated withthyratrons 4CT, SOT and SOT, respectively, for developing cut-off biasfor thyratrons 4CT, 5CT and SGT and consequently preventing firing ofignitrons ATU, STU and STU.

Control of energy transfer between primary 23 and secondary 22E oftransformer |4T depends upon the following factors. Windings 23, |9, 2Band 2| are wound on a common core 30 so that electromagnetic couplingexists between these windings. Winding 26 is wound on an independent andseparate core 3|, which interlinks also with windings I9, 20 and 2|.Accordingly, if all of windings |9, 20 and 2| are open circuited, noelectromagnetic coupling exists between windings 23 and 26, by reason ofthe fact that they are wound on independent cores having no mutual fluxlinkages. On the other hand, completion of the circuits of any ofwindings |9, 20, 2| results in the creation of a flux linkage path, asbetween the cores 30 and 3|, via one of the common windings I9, 20, 2|and consequently as between primary winding 23 and secondary winding 26.

The circuits of one of windings |9, 20 and 2| are completed, however,only when one of ignitrons 4TU, STU, STU, is conductive, and accordinglyfiring of any of ignitrons 4TU, STU, BTU is accompanied by developmentof off-biasing potential at all the thyratrons |CT, 2CT and 3CT.

Conversely, and by virtue of similar reasoning, firing of any ofignitrons ITU 3TU is accompanied by development of oif-biasing potentialat thyratrons 4CT, 5CT, and SCT, which disables the ignitrons 4TU, STU,BTU.

Accordingly, a positively acting interlock is provided, comprisingtransformers |3T and MT, which prevents firing of any of the ignitronsITU, 'ZTU and 3TU while any of ignitrons 4TU, STU and BTU are firing,and vice versa.

Referring now specifically to Figure 2 of the drawings, there isprovided a simplified schematic diagram of the transformer |4T of Figure1A of the drawing. showing the separate cores 30 and 3|, and the controlwindings I9, 20 and 2|, each linking with both of cores 30 and 3|, andproviding a gate for transfer of energy from primary 23 to secondary 25,when and only when the circuit of one of the control windings I9, 20, 2|is completed. The transformer |3T is, of course, identical with thetransformer MT, and accordingly requires no exposition per se.

Referring now to Figure 1B of the drawings, the primary winding 32 of atransformer I5T, connected across one phase of the three phase line LI,L2, L3, supplies control potential for the system over a pair ofsecondary windings 33 and 34. One of the secondaries, 33, supplies A. C.voltage directly across the lines 24, 25 for energizing the primaries 22and 23 of transformers |3T and HT whenever power is available in thethree phase line Ll, L2, L3, Additionally, while secondary 33 isenergized power is supplied to a relay TD which pulls up on the firstapplication of power thereto, closing normally open contacts TD| after atime delay introduced by the dashpot D, applying potential to the line35, which however remains open at contacts 35.

The secondary winding 34 of transformer |5T supplies potential tovarious sequence control circuits and thyratron control tubes, whichcontrol the sequencing of the present system. One portion 31 of thecenter tapped secondary winding 34 is connected in a series circuitcontaining a dropping resistor R2, a variable potentiometer IP, afurther dropping resistor R3, and back to tap 38 of secondary 34. Thevariable arm 39 of the potentiometer IP is connected over a pair ofseries connected resistors R4 and R5 and over normally closed contacts46 and a further dropping resistor R6, to a further terminal 4| ofsecondary winding 34. The point of interconnection of resistors R4 andR5 is connected via a timing circuit consisting of a parallelcombination of resistor R1 and condenser 01 to the control grid 42 of agaseous tacts gized for the remainder of the sequencing operacircuit'forthe cathode of the Thyratron llCT immediately fires, energizingrecontrol .tubeor thyratron ICI, the cathode of which isconnecteddirectlyto the center tap 38 ofthe secondary 3.4 of transformerI51. The

condenser 07 is charged by: gridxconduction, maintaining the grid 2negative. and the thyratron TC?! in a non-conductive condition, thetotal charge on the condenser being a function of the setting of thepotentiometer AP, since this determines the charging potential of thecondenser Cl. Upon closure of the manually or foot controlled startingswitch FS a circuit is completed for the relay 5GB via the line 44, thenormally closed -.contacts 45 of relay IOTD and back to the center tap,38 of secondary 34 via lines Alt and ll. Relay 50R. pulls upestablishing an obvious holding circuit for itself over contacts 5-3andestablishes anode circuits over now closeducontacts it and line 50,for the thyratron 'lCT, via relay lll), for the thyratron 861 via relayMD, and for the thyratron 9C'I' via relay 9T1). Simultaneously, thecontacts 40 open, removing charging potential.

from condenser Cl and; enabling the condenser terminated upon firing ofthyratron TCT and the accompanying relay operation.

Firing of the thyratron 'ICT effects energiaation of the relay lTD,which pulls up and. completes a. circuit for the relay SCH over the cornRelays T'IDand 60R now remain ener tion. Energization of relay SCR opensnormally closed. contacts '52 which are in circuit with the grid-circuitof the thyratron fiCT, opening the latter circuit.

Simultaneously the normally open contacts as of relay I'I'D close,completing an energizing circult for relay lCR, which pulls rip-openingnormally closedcontacts 5d and ill and thereby removingpower from. linepairs Z4, 56 and 25, 5i

which supply oil-biasing signal to transformers IT; 8T, 97. and NET, HT,521 respectively, and

:to associated rectifier units BX, to maintain the ignitrons ITU iiTUall. in unfired condition, for all times prior to the firing ofthyratron ICT, and the consequentenergisation of relay coil. ETD and theclosure of contacts 36.

Simultaneously, the normally open contacts 58 associated with relay 6 3Rclose. establishing a iyratron :lCT.

lay STD, which pulls up, closing normally open contacts 59 andcompleting a circuit from secondary-3.3 over linesfii l and 56, fromwhich branch "lines wand iii lead to the primaries oftransformers l'T,and 9T. These transformers supply current to charge the grid circuits ofthe "i'ihyliatrons iC'l', and tCT-hlocking thelatter "and preventingfiring of the ignitrons lTU, BTU

and IKKEFMTWhflG, ignitrons lTU, 5TH and BTU conduct since no blockingbias is applied to the associated firing tubes 105., ECT and SOT,

the ccnta {52 being now open consequently the lines which complete acircuitfor ener- .gizing ofi-bias generating transformers it'll, HT andIZT, lacing incomplete or open.

Total weld time Conncctedbetvveen line-L- l and line handconsequentlyacross section tl' of secondary 34 of transformer I5T, isprovided a potentiometer circuit comprising in series a potentiometerBP, and a dropping resistor 'iiRl. There is accordingly established atthe variable arm 63 of the potentiometer 8? a potential determined bythe setting of the variable arm The variable arm 63 of the potentiometeris further connected over a pair of resistors in series, to the normallyclosed contacts 52 and thence over normally closed contacts ti lassociated with relay ETD and via line hi) to the terminal ii ofsecondary 34. The voltage present at the junction of resistors SR2 isapplied to charge the weld time condenser #30! by conduction inthyratron ECT, the charge on condenser SCI being of such polarity as tomaintain the grid of thyratron QCT negative, and the thyratron itself inunnred condition. The condenser SCI is of considerable capacity, andacts as a charge reservoir transferring increments if its charge to asmaller capacitor 302 over a resistor in response to closure of normallyopen contacts 65 of relay STD, and the condenser 3C2 itself dischargingover resistor 8123 and via normally closed contacts 65 when relay STD isdeenergised. Resistor 8R3 and capacitor 8C2 are small so that eachpartial discharge of 8C! takes place in a short time interval(substantially instantaneously).

At the time of commencement of a total weld time,'i. e., when relays lTDand 66B, energize, the tube 801' is biased on, and the condenser 8C1 ischarged to a voltage determined by'the settin of potentiometer arm thatpotentiometer 8P. The total weld time terminates upon discharge ofcondenser 8C1 to the extent required to enable firing of thyratron 801,and this time is determined by the relative capacities of conclensersllCl'and i302 and by the total original potential of condenser 8Ci.Discharge of condenser fiCi occurs in successive cycles, a-t'relativelylow frequency, these cycles being established by on off operation offrequency control relay STD and consequent closing and opening ofcontacts 8", and accompanying opening and closing or contacts fit. Eachtime that contacts 65 close a portion of the charge existing oncondenser GCl leaks on to condenser which is or relatively smallcapacity, and each time that contacts 66 close the condenserilCr? isdischarged over its associated resistor in preparation for a furthercharging cycle.

After a predetermined. number of such opera tions, which occur at afrequency determined by timing circuits established in the grid circuitsof thyratron QCT, the condenser iiCl becomes fully and the thyratron tCTfires, completing a total welding time. During alternate err-oiloperations of the relay alternate sets of ignitrons iTU, ZTU, STU andl'lDU, STU, STU are caused to provide current to the Weld, in 0ppositedirections, as will appear as the description proceeds.

The duration of the welding periods and their frequency are determinedby operation of the relay till), the thyratron 3 3T and an on-and-offtiming circuit including a condenser connected in the grid circuit ofthe thyratrcn QCT.

Charging current for the timing condenser 90,

grid circuit of the thyratron 8C? is provided by the secondary windingd9 of a transformer over normally open contacts 61 of relay 9T1 chargingtaking place, while thyratron E-lCTis fired, over potentiometer HP! andby conduction in thyratron ilCT. The total charging time of condenser 86is determined,

accordingly, by the setting of potentiometer SPI. After condenser SC hascharged. for a sufficiently long time interval the grid of thyratron SCTbecomes negatively biased, beyond its critical value, and on asucceeding negative half cycle of potential applied to the thyratron SCTfiring thereof ceases. The relay STD then releases, opening contacts 6'!and closing contacts 68. Condenser SC now discharges throughpotentiometer 9P2 over now closed contacts 68, until the potential inthe grid of thyratron SCT has risen to a value sufficient to enablere-firing thereof. Normally the settings of potentiometers SPI and SP2maybe adjusted to provide equal charge and discharge times for thecondenser SC, so that the half cycles of welding time established by therelay STD will be equal. The time values of half periods, andaccordingly the frequency of the welding cycles, may be adjusted by thejoint settings of potentiometers SP! and SP2.

These potentiometers are so set that relay STD remains in its on and citpositions for intervals determined by the welding frequency de sired.During these on and ofi intervals each group of ignitrons ITU, ZTU andSTU and 4TU, 5TU and STU, respectively, is conductive in its turn. Theon and off intervals are so set that all three tubes of each groupconduct an equal number of times. At the end of the total weld intervalrelay STD drops out-that completes an on interval. Condenser SCI thendischarges into condenser 8C2 and tube BCT becomes conductive. Sincecondenser SCI discharges substantially instantaneously, tube SCT becomesconductive immediately following the dropping out of relay STD and thecurrent flow through the ignitrons is immediately discontinued. The timewhich elapses between the last dropping out of relay STD and the openingof the firing circuits for the ignitrons is so short that the firingcircuits for the ignitrons of the nonconductive group have opened beforethe last ignitron of the conductive group becomes nonconductive.

While the contacts 68 alternately open and close, and the contacts 6!simultaneously close and open, establishing the sub-intervals of thewelding period, the contacts 65 and 66 operate to remove successiveincrements of charge from total weld time capacitor 8C| and the contacts59 and 62 close in alternation to effect firing of the ignitron groupsITU, ZTU, STU and QTU, 5TU, and BTU in alternation by completingcircuits from secondary 38 of transformer I5T to lines 56 and 57 inalternation.

After completion of discharge of total weld time capacitor BCI, thethyratron SCT fires, pulling up the relay STD. Contacts 10 now openbreaking the holding circuit H for the relay ICR. The latter releases,closing contacts 54 and 55 and establishing a lock-out biassimultaneously for all the thyratrons ICT SCT over lines 56 and 51, andterminating the transfer of power to the welding load over that one ofignitrons ITO BTU which last fired, and preventing refiring of any ofthe ignitrons thereafter.

Additionally, the contacts 12 of relay 8DT open, initiating a holdperiod by initiating discharge of a timing circuit in the grid circuitof thyratron I (ICT, and the contacts 64 of relay STD open, breaking thecharging circuit for condenser SCI, and thus maintaining the tube 8CT infired condition.

The condenser MC in the grid circuit of thyratron "ICT is normallycharged over a potentiometer I 0P which establishes a charging potentialfor the condenser 10C. The normal condition of the thyratron IOCT isoff, so long as the relay contacts 12 of STD remain closed. Upon openingof relay contacts 12, at the termination of a weld period, the chargingcircuit is interrupted and the condenser IOC discharges over resistor10R. After an interval determined by the time constant of the circuitcomprising I00 and IR, and by the setting of the potentiometer MP, thegrid of thyratron IOC'I attains firing potential and the thyratron [OCTfires, energizing relay IOTD.

Energization of relay ISTD opens contacts 45, opening the line 44 andcausing deenergization of relay 5CR. The contacts 49 then reopen,breaking the line 50 and removing potential from the plates of thyratroncontrol tubes ICT, STD, STD. Plate potential for control tube IO'I'D ismaintained, however, by a circuit extending over normally closedcontacts 15 and blade 11 of a two position switch 18, line 83, and backto secondary 34 of transformer I5T.

Simulaneously, contacts of relay IO'ID open, removing charging potentialfrom timing circuit HC, HR in the grid circuit of oil thyratron IICT,initiating an oil timing interval. At the same time contacts 82 of relayI OTD open, opening the charging circuit for timing circuit 10C, 10R ata new point, to ofiset the closure of contacts 12, of relay STD whichisdeenergized due to loss of plate potential at the plate of thyratronSCT.

After the off time interval has been completed the thyratron I ICTfires, pulling up relay IITD and breaking the contacts 15, and therebyits own plate circuit and the plate circuit of hold tube IOCT, and bothtubes become non-conductive.

The two position switch 18 performs the function of by-passing thecircuit closer FS in providing a circuit over line 63 for the controlthyratrons [DOT and IICT and. associated relays IOTD and HTD when in theposition illustrated, and supplying operating voltage to the holdcircuit comprising thyratron T and relay ISTD to the exclusion of offrelay l ITD and thyratron IICT when in the alternative position. Whenswitch 18 assumes the position illustrated then, the system operates inrepeated cycles, whereas the alternative position contemplates making ofsingle welds, or non-repeat operation.

The latter operation requires no "ofF time, and each welding operationrequires separate closure of switch F'S. Repeat operation requires theinterposition of an off period between the hold and squeeze intervals.

It is to be understood that the present invention is not limited to theparticular details as described above, since many equivalents for thespecific elements and arrangements utilized in the above disclosure willsuggest themselves to those skilled in the art. While the invention hasbeen disclosed as applied to a welding system, it is susceptible broadlyto use as a system of controlled transmission of power between a threephase power source and a single phase load and addtionally as afrequency changing system for translating the frequency of a source intoa lower frequency having a value which may be selected at will. Varioustypes of tubes may be substituted for the electronic discharge devicesdisclosed and modifications of the specific circuit arrangementsdisclosed may be devised which incorporate the principles of operationset forth in the specific embodiment of the invention herein disclosed.

In view of the above facts, it is desired that the appended claims beaccorded a broad interpretation which is commensurate with the truespirit and scope of the invention within the pertinent art.

Iclaim as my invention:

1. In a system for transmitting power between a source and a load, apair of electric discharge devices connected inversely in parallelbetween said source and said load, means for controlling the conductionof said discharge devices, and means for preventing simultaneousconduction of said discharge devices, including a transformer having,two magnetically independent cores, a first winding on one of saidconnected to a power source, a second wind? on the other of said coresconnected. in the bias circuit of one of said dischargedevices, and. athird. winding common to said independent cores and connected to he energized by conduction of the other or dis charge devices.

2. In a system for transmitting power between a three phase threelinepower source, and a single, phase load, a three-phase to single-phasetransformer having three primary windings and a secondary windin each ofsaid primary windings being connected. across a pair of ii. es of saidthree-phase three-line power source, a pair of ischarge devicesconnected in parallel. re lation in series with each of said primarywindings, a group consisting of one each pair of said discharge devicesconnected to enable transfer of current of one polarity o d s cond arywinding; in a i tor controlling the conduction of group of saiddischarge devices, means to pre. group or discharge devices irornconducting while any one of the other group of said charge devicesconducting, including a transformer having a primary winding connectedto one phase of said power so roe, and a secondary Winding connected inthe bias circuits of one of groups of discharge devicesa first magneticcore for said primary winding nd a second. magnetic core for saidsecondary winding, cores being normally .inagnetica v mutually isolated,a normally opencircuited auxiliary tivinrl 1g wi h each electricdischarge device of a group, and l ring both of magnetic cores, andmeans for closing said normally open-ci cuited auxiliary Windingresponsive to cond tion of the electric discharge device associated.with that winding.

In a system for tran itting power setween a three-phase three-line powersource, a sin- ,le-phase load, a to si gle-phase transformer havingthree windings and a secondary winding, each of said primary wind ingsbeing: connected across pair of lines of said three phase three-linepower source, a pair of discharge devices having a principal anode andan auxiliary anode, and a cathode connected in inverse parallel relationin series with each of said primary windings, a group consisti of one ofeach pair of said discharge devices being connected to enable transferof current of one polarity to said secondary winding in a first phase,means for controlling the conduction of each group of said dischargedevices, and mean to prevent any one of one group of saiddischargedevices from conducting while any one of theothei' group .of.saiddischarge devices is conducting,

t any one of one (ill 14 including a transformer having-ya primary windlug connected to one phase of said power source. and a secondary windingconnected inthe-bias ciiits of of said groups of discharge devic .s,first magnetic core for said 1 marywinding and a second magnetic corefor-said secondary winding, said cores being normally magneticallymutually isolated, a normally open-circuited auniliary Winding connectedbetween the auxiliary anode and the cathode of each of saidwdischargedevices, and linking hoth of said magnetic cores.

.4. In a system for transmitting power from a source to a load, aplurality of electric discharge devices connected inversely in parallelbetween said'source said load, means forcontrolling conduction ofdischarge devices, means to prevent simultaneous conduction of saiddischarge devices of opposite polarity, including a pair of transformerseach having two magnetically mutually isolated cores, a Winding on oneof said cores connected to said source, a winding on the other of coresconnected in the bias circuits of said discharg devices of polarity, anda plurality of windings linking both of said cores, each of saidplurality being connected to he energized. responsive to conduction of adischarge device of other polarity.

v5. In a system for transmitting power from a source to a load, atransformer having a primary winding connected with sai 1 source and asecondary winding connected with said. load, a first magnetic core forsaid primary winding and a second magnetic core for saidsecondarywinding, said cores being normally magnetically mutuallyisolated, .a normally open-circuited auxiliary winding linking both saidmagnetic cores, and means for closing the circuit of said normallyopen-circuited auxiliary winding comprising an arc discharge device pathfor transmitting' current between said source and said load, said aredischarge device path comprising a path between an auxiliary anode and acathode of an arc discharge device having a further anode and havingmeans for establishing arc between-said further anode and said cathode.

t. In a timing system for timing transfer of current from a three phasesource to a single phase load, a first group of are discharge deviceseach connected in current controlling relation between one phase of saidthree phase source and said single phase load,a further group of arcdischarge devices each connected 1 A current controlling relationbetween one of said three phase source and said load, each of said firstgroup of arc discharge devices being connected in inverse parallelrelation with an arc discharge device of said-further group of arcdischarge devices, are discharge devices of one of said groups losingall arranged to transfer identically directed current in said load; afirst group'of firing valves for said first group of arc dischargedeviceaa second group of firing valves for said second group of arcdischarge devices, first means for developing hold-off bias forsaidfirst group of firing valves for preventing firing operation of all thearc discharge devices of said first group of arc discharge deviceswhensaid second group of discharge devices are concluc tive, second meansfor developing hold-oil bias for said second group of firing valves forpreventing firing operation of all the arc discharge devices of saidsecond group of arc discharge devices when said first group of dischargedevices are conductive, means for periodically actuating said firstandsecond means in alternation for aprodetermined number ofalternations, and means thereafter operative for actuating first andsecond means simultaneously, said means for periodically actuating saidfirst and second ears comprising a timing circuit having a first timingcondenser, means responsive to a predetermined variation of charge insaid first timing condenser for actuating said first means, and meansresponsive to a further variation of charge in said first timingcondenser for actuating said second means.

7. In a timing system for timing transfer of current from a three phasesource to a single phase load, a first group of arc discharge deviceseach connected in current controlling relation between one phase of saidthree phase source and said single phase load, a further group of arcdischarge devices each connected in current controlling relation betweenone phase of said three phase source and said load, each of said firstgroup of arc discharge devices being connected in inverse parallelrelation with an arc discharge device of said further group of arcdischarge devices, are discharge devices of one of said groups being allarranged to transfer identically directed current in said load, a firstgroup of firing valves for said first group of arc discharge devices, asecond group of firing valves for said second group of arc dischargedevice first means for developing hold-ofi bias for said first group offiring valves for preventing firing operation of all the arc dischargedevices or" said first group of arc discharge devices when said secondgroup of discharge devices are conductive, second means for developinghold-01f bias for said second group of firing valves for preventingfiring operation of all the arc discharge devices of said second groupof arc discharge devices when said first group of discharge devices areconductive, means for periodically actuating said first and second meansin alternation for a predetermined number of alternations, meansthereafter operative for actuating said first and second meanssimultaneously, said means for periodically actuating said first andsecond means comprising a timing circuit having a first timingcondenser, means responsive to a predetermined variation of charge insaid first timing condenser for actuating said first means, and meansresponsive to a further variation of charge in said first timingcondenser for actuating said second means, and wherein is fur therrovided a second timing condenser having a predetermined charge, meansfor varying said charge in the same sense in successive discretequantities of charge, and means responsive to a predetermined totalvariation of said predetermined charge for actuating said first andsecond means simultaneously and for disabling said timing circuit.

8. In a timing system for timing transfer of current from a three phasesource to a single phase load, a first group of arc discharge deviceseach connected in current controlling relation between one phase of saidthree phase source and said single phase load, a further group of arcdischarge devices each connected in current controlling relation betweenone phase of said three phase source and said load, each of said firstgroup of arc discharge devices being connected in inverse parallelrelation with an arc discharge device of said further group of arcdischarge devices, arc discharge devices of one of said groups being allarranged to transfer identically directed current in said load, a firstgroup of firing valves for said first group of are discharge devices, asecond group of firing valves for said second group of arc dischargedevices, first means for developing hold ofi bias for said first groupof firing valves for preventing firing operation of all the arcdischarge devices of said first group of arc discharge devices when saidsecond group of discharge devices are conductive, second means fordeveloping hold-off bias for said second group of firing valves forpreventing firing operation of all the arc discharge devices of saidsecond group of arc discharge devices when said first group of dischargedevices are conductive, means for periodically actuating said first andsecond means in alternation for a predetermined number of alternations,means thereafter operative for actuating said first and second meanssimultaneously, said means for periodically actuating said first andsecond means comprising a timing circuit having a first timingcondenser, means responsive to a predetermined variation of charge insaid first timing condenser for actuating said first means, and meansresponsive to a further variation of charge in said first timingcondenser for actuating said second means, and wherein is furtherprovided a second timing condenser having a predetermined charge, meansfor varying said charge in the same sense by successive discretequantities of charge, and means responsive to a predetermined totalvariation of said predetermined charge for actuating said first andsecond means simultaneously and for disabling said timing circuit andwherein is still further provided means responsive to transfer of cut byany are discharge device of one of said groups of arc discharge devicesfor actuating that means for developing hold-off bias which controls thealternative group of arc discharge devices.

9. In a timing system for timing transfer of current from a three phasesource to a single phase load, a first group of arc discharge deviceseach connected in current controlling relation between one phase of saidthree phase source and said single phase load, a further group of arcdischarge devices each connected in current controlling relation betweenone phase of said three phase source and said load, each of said firstgroup of arc discharge devices being connected in inverse parallelrelation with an arc discharge device of said further group of arcdischarge devices, are discharge devices of one of said groups being allarranged to transfer identically directed current in said load, a firstgroup of firing valves for said first group of arc discharge devices, asecond group of firing valves for said second group of arc dischargedevices, first means for developing hold-off bias for said first groupof firing valves for preventing firing operation of all the arcdischarge devices of said first group of arc discharge devices when saidsecond group of discharge devices are conductive, second means fordeveloping hold-off bias for said second group of firing valves forpreventing firing operation of all the arc discharge devices of saidsecond group of arc discharge devices when said first group of dischargedevices are conductive, means for periodically actuating said first andsecond means in alternation for a predetermined number of alternations,means thereafter operative for actuating said first and second meanssimultaneously and means responsive to firing condition of an arcdischarge device of one of said groups of arc discharge devices foractuating that one of said first and second means which prevents firingof the remaining group of are discharge devices.

JOHN R. PARSONS.

References Cited in the file of this patent 5 UNITED STATES PATENTSNumber Name Date Kouyoumjian Nov. 3, 1931 Overbeck Sept. 15, 1942 10Number 18 Name Date Braaten Jan. 5, 1943 Leathers et a1. Aug. 29, 1944.-Livingston Sept. 18, 1945 Mumma June 18, 1940 Overbeck July 30, 1 046Sciaky Nov. 18, 1947 Beamer Mar. 15, 1949 Andresen June '7, 1949

